A droplet jetting apparatus used in a known inkjet print head squirts a small amount of ink to the outside through a nozzle by heating a heater or applying physical force such as pressure by a piezoelectric element or electrostatic force to an ink chamber in which ink is stored. The droplet jetting apparatus is classified into a heating type, a piezoelectric type, a thermal compress type, and an electrostatic force type according to how the physical forces are applied to the ink.
Among the droplet jetting apparatuses of the various types, the thermal compress type droplet jetting apparatus is shown in FIG. 10. As shown in the figure, conventional droplet jetting apparatus of thermal compress type is constituted of a driving unit 20, a membrane 30 and a nozzle unit 40.
The driving unit 20 includes an oxide film 14 laminated on a substrate 15, a working fluid barrier 25 having a working fluid chamber 27, a heater 16 interposed in the working fluid chamber 27 and a wire 17 connected to the heater 16.
The nozzle unit 40 includes an ink chamber barrier 45 having an ink chamber 57 and a nozzle plate 47 connected to the top of the ink chamber barrier 45. A nozzle hole 49 for jetting the ink in the ink chamber 57 is formed on the top surface of the nozzle plate 47.
The membrane 30 is interposed between the ink chamber barrier 45 and the working fluid barrier 25 to partition the working fluid chamber 27 and the ink chamber 57.
In this configuration, the working fluid chamber 27 is charged with the working fluid such as heptane and the ink is continuously supplied to the ink chamber 57 from an ink supply source not shown.
When a current is supplied to the heater 16 through the wire 17, the heater 16 generates heat and the working fluid in the working fluid chamber 27 is heated by the heat, thereby generating bubbles. The internal pressure of the working fluid chamber 27 is increased by the bubbles and the membrane 30 is curved upward. As a result, the inside of the ink chamber 57 is pressurized and the ink is discharged through the nozzle hole 49.
In this state, when the current supply to the heater 16 is stopped, the bubbles are condensed. Accordingly, the membrane 30 is restored and the pressure in the ink chamber 57 lowers. At this time, an ink droplet is exposed outside the ink chamber 57 while the ink exposed to the outside through the nozzle hole 49 is cut off. As the heating operation of the heater 16 is repeated in the above-mentioned manner, the ink is discharged.
However, in the above-mentioned conventional droplet jetting apparatus, the ink can be discharged in the nozzle hole by the bubbles of the working fluid generated by the heat of the heater, and thus color denaturation of the ink could be incurred due to the heat. Further, since separate manufacturing processes for forming the heater, the working fluid barrier and the membrane are required, and each of the constituent members including the nozzle hole, the ink chamber and the like are formed individually, the manufacturing process is also not easy.